Calcium is an essential macro nutrient for plant growth. Calcium is needed by plants for cell growth and division, for the growth of root tips and shoot tips, the retention of leaves and as an integral part or the cellular structural integrity. Efforts to supply calcium in a fertilizer have been complicated by the poor alkaline solubility of calcium salts. This poor solubility leads to problems in storage due to product instability and in application where calcium precipitates can clog irrigation drip feed lines. Prior attempts to solve these problems have produced solid formulations, which require the inconvenience and time to solubilize these solid formulations on site. See for example, U.S. Pat. Nos. 5,171,349, 5,395,418 and 6,312,493.
Attempts to provide aqueous, calcium-based fertilizers have relied on soluble calcium salts that result in an acidic formulation. As an example, see U.S. Pat. No. 5,997,602 which describes various aqueous fertilizer suspensions that have a pH in the range of 0.5 to 2. These formulations also use soluble calcium salts which can readily and rapidly leach from the soil. Another disadvantage is that these low acid formulations may exacerbate acid soil conditions and the effects of the ever-more-common acid precipitation. Yet another disadvantage of these types of aqueous calcium fertilizers is the relatively low concentrations of calcium that can be achieved with the use of soluble salts.
An attempt to prepare a stable aqueous fertilizer suspension that provides sufficient nitrogen, phosphorus, and potassium (referred to as “NPK” materials) in addition to other plant micronutrients such as calcium and magnesium is described in U.S. Pat. No. 5,851,260. This patent teaches fertilizer suspensions that have a pH in the range of 2 to less than 7 and that have a particle size of less than 50 microns and more preferably 0.2-20 microns. This approach requires extensive and costly processing that includes at least two millings to produce very small suspendable particles. This approach also has the disadvantages of requiring significant manufacturing effort and of producing a surface crusting and slight precipitation of the ingredients.
As such, it would be desirable to provide an aqueous, non-acidic calcium-based fertilizer that will not leach from the soil and provide neutralization of the acidity in the soil and precipitation. As used herein, “non-acidic” refers to any neutral or alkaline composition having a pH in the range of 7.0 to 14.